1. Field of the Invention
This invention relates to filter presses, specifically presses having a plurality of filter plates adapted for removing or separating solids from liquids. More particularly, this invention is directed to apparatus for separating the filter plates within a filter press, for removal of filter cake from plate filter cloths and for washing the filter cloths in situ on the filter plate.
2. Statement of the Art
The type of apparatus, known generally as a filter press, is well known in the art. These apparatus are used in various industries to separate solids from liquids. Filter presses may be used to separate solids from suspensions, slurries, and similar aqueous feed streams. Filter presses find application in a variety of chemical and metallurgical industries, e.g. sewage sludge treatment and ore dressing operations.
A filter press generally includes a plurality of separable plates. These plates are slidably held on a frame structure between a fixed support and an opposing moveable support. This moveable support is actuated typically by a hydraulic ram.
The plates are typically arranged in parallel about a horizontal axis. Each plate includes a depression on its side surface. Positioned over that depression is a filter cloth or fabric. Upon the plates being positioned adjacent one another, the opposing depressions in adjacent plates form a cavity wherein the filter cloth is suspended. In order to effect filtering, the plates are compressed one against another and against a fixed end support on the filter by a horizontally mounted hydraulic ram and press head acting against a follower plate. The compression of the plates, one against another, serves to form a sealed abutment of each plate against its neighboring plates. Thereafter, the fluid or solution, to be processed, may be injected into the plates and through the various cavities defined by the adjacent filter plates. Since the feed stream is fed under pressure into the enclosed cavities, the pressure of the feed stream forces the liquid through the filter cloths. The solids within the stream are embedded on the filter cloths as the liquid passes through the cloths.
When the filtering operation is complete, the hydraulic ram is retracted, the plates separated one-by-one, and the cake forced off the filter cloth by pressurized air admitted to the filter plate interior.
As the filtering plates filter the aqueous feed stream, an increasing quantity of solid material is built up upon the surface of the filter cloths. After reaching a certain quantity, these solid deposits or cakes preclude operation or use of the filter. In order to continue use of the filter press, the filter plates must be separated one from another and the cakes or solid deposits removed from the filter cloths.
Subsequently, it is desirable to wash the filter cloths in situ. This has been done commercially in various shifters by providing a washer unit which travels on an overhead beam and trolley system that can be designed to service a series of presses. As the washer unit moves along an overhead beam, the spray head is in retracted position. When the press is opened and the movable head, or follower, has been rolled back to provide an opening between the first two plates, the washer unit is activated. The spray head descends and then rises between the two plates that form the first chamber, spraying as it moves. The filter cloths covering the two opposing plates are subjected to high-pressure water spray from 24 to 40 nozzles. The travel speed of the spray head is adjustable.
After the spray head has been retracted, the washer unit travels along the overhead beam until it is in position to service the second chamber In automatic operation, the movement of the washer unit is synchronized with the action of the plate mover as it opens chamber after chamber. In semi-automatic operation, the action of the washer unit is pendant controlled.
In such washer unit, a pair of long vertical guide rods are attached to a spray head and are guided through apertures in a cross member movable along the fixed overhead beam. In a retracted position, the rods and spray head are moved to a position above the plates so that it can be moved between a different set of plates for a subsequent cleaning cycle. Spray water piping comprises a pair of elongated bellows-like tubing which is compressed in retracted position and is expanded as the spray head moves downwardly to spray each lateral increment of facing fabric cloths. The above construction is exemplified in the Shriver Scourshower washer.
Other filter cloth washers have been constructed in which a spray head washes both sides of one plate at the same time with the spray bar being lowered and raised by cables wound on and wound off a top horizontal cable drum.
The means and method of separating the filter plates one from another to facilitate the cleaning of the filter cloths is a problem which has confronted the industry for many years.
Various attempts have been made in the past to devise automated separation systems for use in separating the plates in the filter press after filtration has been effected.
Representative of some of these attempts are those which are described in U.S. Pat. No. 4,102,788 (Broad), U.S. Pat. No. 4,359,385 (Krivec), U.S. Pat. No. 3,915,863 (Busse, et al.), U.S. Pat. No. 3,232,435 (Fismer), U.S. Pat. No. 4,272,376 (Schotten), U.S. Pat. No. 4,132,647 (Sakuma) and U.S. Pat. No. 4,105,560 (Fismer). In the related application, rodless cylinders extend horizontally along the bottom sides of the filter press frame and in combination with a pawl subsystem, provide for opening of the plates, movement of a sullied plate, i.e. a plate having its fabric media soiled by residual filter cake, an air blow discharge of the filter cake from each plate, and movement of the plate from which cake has been discharged to a follower. After all the plates have had their cake discharged, the follower is activated and the stack of plates returned to abutment with each other for start of a subsequent filter cycle of a feed slurry.